The shape of a face having a change in expression may be estimated in order to find out an emotion or a state of a person. When a driver feels drowsy while driving a car, a change in expression such as frown, puckered lips or puffed cheeks during deep breathing may appear on his face, for example. Accordingly, these changes in expression can be used as an index for checking the drowsiness of the driver.
In a method according to related art, for estimating face shape that has been used, in order to improve the accuracy in estimating the face shape, a face shape is estimated under a constraint that each facial part, that is, eyes, nose, mouth, or others is in its standard shape and position when the person is expressionless. However, with the face shape estimating method, a face in which the change in expression described above is observed but is away from a standard shape cannot be detected due to the constraint. Note that, the expression “change in expression” used herein refers to a state where the face is not expressionless.
In contrast, according to the technique disclosed in NPL1 (hereafter related art 1), the shape and the position of the facial parts when the expression changes can be detected by previously learning an image of a face in which a change in expression has occurred. In addition, according to the technique disclosed in PTL1 (hereafter related art 2), measurement of a three dimensional position of a facial part is performed, and a stereoscopic shape of the face is estimated from the three dimensional position of the facial part. With these operations, the techniques disclosed in NPL1 and PTL1 are capable of detecting a face in which the change in expression described above is observed.